[sdiy] ASM1 VCO

[Gene Stopp]

Seems to me the sawtooth discharge is staying on too long. The discharge FET
is controlled by the LM311 comparator, and the on-time of the reset pulse is
set by an 18pf cap (if I remember right). This is a pretty tiny cap, so I'd
do the following:

a) make sure the cap is really 18pf
b) de-flux the circuit board

To de-flux, get some 100% isopropyl alcohol (like from the electronics
store) and an old clean toothbrush. Turn the board solder-side up, pour
enough alcohol on it to cover the whole board, and start brushing away for a
couple of minutes. Wait for it to dry, then do it again. When it's
completely dry again, power up and look again. Heads up: don't do this over
a nice floor. Seems like a lot of alcohol will go on the ground, but it's
worth it. I do it in the garage. Outside would be better - this stuff is
flammable.

At what frequency does this waveform appear? Is the flat spot a constant
size, so that a lower frequency setting is more sawtooth-like?

Also I'd just like to say "keep it up". When I got my first Electronotes
circuits on PCB's from Wasatch Music in 1974, none of them worked at first
and I knew nothing about electronics. After some time and perserverence they
were all working, and still do to this day. It sounds funny but it's like
riding a bike. I pretty much learned everything I know about electronics
from that experience. When I finally got my degree I aced everything because
I already knew it.


- Gene


-----Original Message-----
From: Josh Randall [mailto:jorandal at vt.edu]
Sent: Thursday, March 28, 2002 3:49 PM
To: synth-diy at dropmix.xs4all.nl
Subject: [sdiy] ASM1 VCO


I finally got the VCO for my ASM1 to work and am very excited.  When I
hooked it up to my Oscope I got a waveform like the following:
\          \          \
 \          \          \
  \          \          \
   -------    --------   --------
I get a line sloped down then it is flat then another downward voltage
then flat.  Does anybody know what could cause the shape of my wave to be
off?

Thanks.

Sincerlly,

Josh Randall